U.S. Pat. No. 4,360,226, the disclosure of which is incorporated herein, considers at length the the tubular mechanical connector prior art and in particular of flexible connectors enabling relative angular movement. Many of the design criteria for high strength flexible connectors set forth therein was at least partially influenced by the desire to provide a capability for a contained inner fluid flow path. While the disclosed connector was primarily directed to an application or use as a marine riser, other applications and uses for that invention such as the present instance were specifically contemplated.
The search for hydrocarbon reservoirs under the ocean floor has now extended to areas beyond the capability of proven existing technology to locate and recover. Extreme wave and weather conditions coupled with even greater water depth has made both conventional fixed platform and subsea completions economically or technically unfeasible in certain instances. To overcome the limitations and disadvantages of conventional equipment, new concepts of a suitable work environment are continuously being developed to provide a suitable working platform to locate and produce the hydrocarbons.
One concept now receiving serious attention is the tension leg platform commonly referred to as a TLP. Rather than being fixed to and supported from the ocean floor as are conventional platforms, the tension leg platform is a floating assembly that is anchored to the ocean floor using an array of redundant anchor support legs that are maintained under tension to hold proper platform location. Unlike floating semi-submersible platforms which are either loosely anchored or dynamically positioned such that they move over a relatively large water surface area by the influence of wind and tide, the tensioned leg platforms are tightly secured by the tensioned legs to severely limit their movement range. With the floating platform construction, the tension legs can be released from their anchors and the platform towed from one operating site to another as desired. This multiple use capability greatly enhances the use economics and makes this type of platform particularly attractive for economically marginal hydrocarbon production situations.
The tensioned legs are anchored at one end to the ocean floor when the platform is operational. Normally, the securing anchors are permanently set on the ocean floor, but retrievable anchors may be used if desired. After a leg anchor is set on the ocean floor, the tension leg is extended from the platform to connect with the anchor using the mechanical connector of the present invention. Normally, redundant legs are extended in each anchoring direction from the floating platform. The connector mechanically attaches or secures each tension leg to an anchor, but may be released and the associated tension leg and connector retrieved for inspection as desired.
As the name so indicates, the platform legs are subjected to a large axial tension stress loading to maintain proper platform position. Because of this large tension loading, the legs are normally made relatively massive and heavy to provide a low stress level. Due to the resulting great weight of the legs, the mechanical connectors are set or actuated for securing by the weight of the tension leg being received or transferred to the anchor. In addition, weight set mechanical connectors are not normally acceptable unless the anchor engageable tension load bearing connector member is arranged to prevent damage to the permanently set anchor portion of the connector when connecting. During extreme sea or wind conditions, it is possible that a platform tension leg would be subjected to a short period of compression force loading. The possibility that such a compression loading condition may exist, even for a very brief period, excludes use of mechanical connectors that are released by a down and then up sequence of manipulation of the tubing leg.
Preferably, redundant remotely controlled release mechanisms are provided in each connector to insure separation when desired. It is also desirable that all of the operating or working parts of the mechanical connector be retrieved to the platform with the tension leg member for inspection and repair. Because of the undesirable features or shortcomings of the prior connector devices, their use in tension leg platform applications has been largely precluded.
To minimize bending and other undesired stress buildup in the tension legs, a flexible joint is preferably located in the tension legs adjacent the releasable mechanical connectors. If desired, a second flexible joint may also be disposed between the releasable connector and the anchor. The preferable flexible connectors utilized are similar to those disclosed in U.S. Pat. No. 4,360,226, identified above and which provide a central passageway through which an operating tool or controlled flow may pass.